Narrowing of generic this is inconsistent with variable narrowing

### 🔎 Search Terms

generic union constraint narrowing this

### 🕗 Version & Regression Information

- This is the behavior in every version I tried

### ⏯ Playground Link

https://www.typescriptlang.org/play/?noImplicitReturns=false#code/C4TwDgpgBAKu0F4oEkDMAmKAfKBlYATgNwBQAlgHbAQEBmAhgMbT4FQDeJUUA5gQPYBXMAC4oAIgr8KEcaW4BrSgBMx4gM6E5JAL7kqNBsxQYOXXgOFr1jegBt6BbYpVqyGbXpLKIjBwWhaQQpGYDJpKGB6BQg0dAAKADd7QQgxOIBKMUT+MmVSHz9HQODQ8IooSloaAGkVAB4YAD4klLSOKCUKVVgoHSzYUhIgkLCI6k0YAAsydUaoCAAPam71WHgW4Bn1MRgMs251AHcyYEYpqHit2YA6PiEwfc5ublt1aElpWRFzF6gA4CCAgUeQvN4fGz2RziH5-Q4nM4XK7bG5dZRPX5w8ESTROMQAenxUCkCwIAgIAH5MX9seJ3OgYdS+uY9F4RmVxhBNAAFRz0AC2EGoBHmSxWyjWcEgLX4uwx8NO50u-DulkeBzB9HeEikMkZcP+QqBIMxtMh-n1cOOiqRKrR8oNUDNWgJRJo5IAhEzXlqPvTLX89NxWSRhqUxhUJsAAIJ2Mi+5TTWai5YQVbraXI2ZyjWMaSaKD8KBIa7qUHWxHK1UPB0+7WfPWwuEA42gusQ2wWpt-CtK+J2lS1rG+nEuqCE0me71Okd0jzdl5B5ls8PlSJc4BJ9ToFPiyUbLM7WADOLYKDBHy0SgQZQasi0S6l6vCYsIJAaTvQod5igF5J2VJ0lMEttiIcc3TJfgCExKIYjiQ8MjAid3SgmDtigdR6DCdQry5Ex0CQiDyVNfNgCgRwBCOYtLhPYCmkiUDwMnVC-hbYEGNmQjmOg4NdFDdkI3XHk+UFYUdxgBZU3TKUIBlOUgMwHALwgK8ZFvZ5KgfftnzAV933NL8NVeUioH-QD8Oo-guP4BQYOiWIMH7RCmJszEi0w7DcLWOJrNsmkTIo-gqKQeJaMwBB6Ksly-JeNiKiiidXN4ldRjXKNY3jd5E22cTJL3DNZMPeSLKU7oVOvdTzB-AsixAzjzHvKt7hfN99M-JxvxMsz2lPJAEqJJKXlghyEn4ZzEpi7h3Kw2YvPw3ySN-MjAuCmiFOLSKFtYo12P6wsYpDIA

### 💻 Code

```ts
type Type = I32 | Str;
interface Str {
group: "none";
kind: "str";
}
interface I32 {
group: "scalar";
kind: "i32";
}

declare function takeI32(value: I32): void;
declare function inferKind(value: { kind: T }): T;

function testThis(this: T) {
switch (this.group) {
case "none":
return;
case "scalar":
switch (this.kind) {
case "str": // no error?
case "i32":
}
}
}

function testParameter(o: T) {
switch (o.group) {
case "none":
return;
case "scalar":
switch (o.kind) {
case "str": // error!
case "i32":
}
}
}

function testAliasedThis(this: T) {
const o = this;
switch (o.group) {
case "none":
return;
case "scalar":
switch (o.kind) {
case "str": // error!
case "i32":
}
}
}

function testThis2(this: T): I32 | undefined {
if (this.group === "scalar") {
const value: I32 = this; // error
takeI32(this); // error
this satisfies I32; // error
const arrow = (): I32 => this; // error
return this; // error
}
}

function testParameter2(o: T): I32 | undefined {
if (o.group === "scalar") {
const value: I32 = o; // ok
takeI32(o); // ok
o satisfies I32; // ok
const arrow = (): I32 => o; // ok
return o; // ok
}
}

function testAliasedThis2(this: T): I32 | undefined {
const o = this;
if (o.group === "scalar") {
const value: I32 = o; // ok
takeI32(o); // ok
o satisfies I32; // ok
const arrow = (): I32 => o; // ok
return o; // ok
}
}

```

### 🙁 Actual behavior

The errors (or lack of them) are inconsistent between narrowing `this` directly vs narrowing an "aliased" `this` (`const alias = this;`)

### 🙂 Expected behavior

They should be consistent

### Additional information about the issue

_No response_

Start with the linked TypeScript Playground and reduce the provided generic-union examples for direct this, aliased this, and parameter narrowing. No repository file or test is identified in the issue, so locate the compiler narrowing entry point and add a regression test covering the shown cases. Done means direct and aliased this narrowing produce consistent diagnostics.

Written by the indexing model from the issue text.